This invention relates generally to shoe soles and more particularly to flexible shoe soles which have additional cushioning for the ball and/or heel of the foot.
A foot absorbs most of the load when walking or running in the ball and heel of the foot. The natural construction of the foot is well suited to absorb these forces when on relatively soft surfaces (e.g., grass or soft earth) or when the activity is relatively short in duration. However, when moving about on hard surfaces (e.g., roads and floors), particularly when the movement is sustained or high loads are encountered as in an athletic endeavor, the load becomes so great as to cause discomfort and injury to the foot. The location of the discomfort and injury is frequently one of the load bearing ball and heel regions of the foot.
The problem of protecting the ball and heel of the foot has been frequently addressed in the prior art by simply providing a shoe having additional cushioning in either or both the ball and heel regions of the shoe sole. However, the transmission of the cushioning effect to the foot has heretofore been limited. The cushions have been confined to the portions of the sole beneath the insole. The insole is a substantially rigid, hard piece constructed to withstand forces caused by connection of the upper which tend to deform the insole. As a result of the construction of the insole, the foot is significantly shielded from the cushioning effect by the insole. Moreover, the insole tends to inhibit flexibility of the shoe.
Although existing shoes provide substantial cushioning of the foot in the ball and heel regions, they tend to limit the foot's natural flexing motion when walking or running. The primary sources for rigidity of the shoe are the outsole and the insole. The outsole must be sufficiently robust to withstand the wear associated with contacting the ground. Generally speaking, the more robust materials tend to be less flexible. The insole tends to be rigid because it must withstand forces tending to deform the insole which are caused by the connection of the upper to the sole.